linux-kernel - Re: [PATCH 3/3] perf hist stdio: Do bounds check when printing callchains to avoid UB with new gcc versions

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Message-ID: <Z9KJQdUkEel3OP1X@google.com>
Date: Thu, 13 Mar 2025 00:29:05 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	James Clark <james.clark@...aro.org>, Jiri Olsa <jolsa@...nel.org>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Clark Williams <williams@...hat.com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 3/3] perf hist stdio: Do bounds check when printing
 callchains to avoid UB with new gcc versions

On Mon, Mar 10, 2025 at 02:55:52PM -0700, Namhyung Kim wrote:
> On Mon, Mar 10, 2025 at 04:45:33PM -0300, Arnaldo Carvalho de Melo wrote:
> > From: Arnaldo Carvalho de Melo <acme@...hat.com>
> > 
> > Do a simple bounds check to avoid this on new gcc versions:
> > 
> >   31    15.81 fedora:rawhide                : FAIL gcc version 15.0.1 20250225 (Red Hat 15.0.1-0) (GCC)
> >     In function 'callchain__fprintf_left_margin',
> >         inlined from 'callchain__fprintf_graph.constprop' at ui/stdio/hist.c:246:12:
> >     ui/stdio/hist.c:27:39: error: iteration 2147483647 invokes undefined behavior [-Werror=aggressive-loop-optimizations]
> 
> Hmm.. does it warn about a signed integer overflow?
> 
> 2147483647 is 0x7fffffff in hex and it should be INT_MAX.
> I'm not sure what is the problem.

Maybe the aggressive loop optimization can unroll the loop more than the
INT_MAX...?  Anyway the fix is simple and makes sense.

> 
> 
> >        27 |         for (i = 0; i < left_margin; i++)
> >           |                                      ~^~
> >     ui/stdio/hist.c:27:23: note: within this loop
> >        27 |         for (i = 0; i < left_margin; i++)
> >           |                     ~~^~~~~~~~~~~~~
> >     cc1: all warnings being treated as errors
> >     --
> >     util/units.c: In function 'unit_number__scnprintf':
> >     util/units.c:67:24: error: initializer-string for array of 'char' is too long [-Werror=unterminated-string-initialization]
> >        67 |         char unit[4] = "BKMG";
> >           |                        ^~~~~~
> >     cc1: all warnings being treated as errors
> 
> This part belongs to the previous commit. :)

I'll drop this part.

Thanks,
Namhyung

> 
> > 
> > Cc: Adrian Hunter <adrian.hunter@...el.com>
> > Cc: Ian Rogers <irogers@...gle.com>
> > Cc: James Clark <james.clark@...aro.org>
> > Cc: Jiri Olsa <jolsa@...nel.org>
> > Cc: Kan Liang <kan.liang@...ux.intel.com>
> > Cc: Namhyung Kim <namhyung@...nel.org>
> > Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> > ---
> >  tools/perf/ui/stdio/hist.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/tools/perf/ui/stdio/hist.c b/tools/perf/ui/stdio/hist.c
> > index 74b2c619c56c8ba3..7ac4b98e28bca82e 100644
> > --- a/tools/perf/ui/stdio/hist.c
> > +++ b/tools/perf/ui/stdio/hist.c
> > @@ -1,4 +1,5 @@
> >  // SPDX-License-Identifier: GPL-2.0
> > +#include <limits.h>
> >  #include <stdio.h>
> >  #include <stdlib.h>
> >  #include <linux/string.h>
> > @@ -24,6 +25,9 @@ static size_t callchain__fprintf_left_margin(FILE *fp, int left_margin)
> >  	int i;
> >  	int ret = fprintf(fp, "            ");
> >  
> > +	if (left_margin > USHRT_MAX)
> > +		left_margin = USHRT_MAX;
> > +
> >  	for (i = 0; i < left_margin; i++)
> >  		ret += fprintf(fp, " ");
> >  
> > -- 
> > 2.48.1
> >